Fluid pump

ABSTRACT

A fluid pump includes an inlet; an outlet; a motor; and an impeller rotated by the motor about an axis, the impeller being positioned axially between an inlet plate and an outlet plate. The inlet plate includes a channel that receives fluid from the inlet, the channel being defined by an inner wall and an outer wall. The channel has a first region extending over an angle of at least 150° and a second region extending from the first region over an angle of 61.8° to 71.8°. The inner wall has a first radius centered about the axis which is constant over the first region and the second region. The outer wall has a second radius centered about the axis which is constant over the first region and also has a third radius not centered about the axis which is constant over the second region.

TECHNICAL FIELD OF INVENTION

The present invention relates to a fluid pump; more particularly to afuel pump; even more particularly to a fuel pump with an electric motorwhich rotates an impeller that is located axially between an inlet plateand an outlet plate; and still even more particularly to an inlet plateflow channel of the inlet plate which minimizes noise due to structuralvibrations induced by fluid hammer at the end of the inlet plate flowchannel.

BACKGROUND OF INVENTION

Fluid pumps, and more particularly fuel pumps for pumping fuel, forexample, from a fuel tank of a motor vehicle to an internal combustionengine of the motor vehicle, are known. U.S. Pat. No. 6,824,361 to Yu etal. shows a typical electric fuel pump which includes and impeller witha plurality of blades that is located axially between stationary inletand outlet plates. The inlet plate includes an inlet which allows fuelto enter the fuel pump such that the inlet is in fluid communicationwith an inlet channel formed in a face of the inlet plate that facestoward the impeller. The inlet channel is arcuate in shape such that theinlet opens into a first end of the inlet channel and such that fuelflows from the first end to a second end of the inlet channel when theimpeller is rotated by an electric motor of the fuel pump. Fuel thatreaches the second end of the inlet channel is pushed through spacesbetween the blades of the impeller and into an outlet channel formed ina face of the outlet plate that faces toward the impeller. One end ofthe outlet channel includes an outlet passage which extends axiallythrough the outlet plate. Consequently, the fuel that has beenpressurized by the impeller passes through the outlet passage and pastthe electric motor to an outlet of the fuel pump. Motion of the bladesof the impeller causes fluid pressure fluctuations which in turn causesvibration of the inlet plate which propagates through the rest of thestructure of the fuel pump. Furthermore, when the fuel reaches the endof the inlet channel, a fluid hammer effect may be produced, therebyresulting in a high frequency noise that may be objectionable. While notshown in U.S. Pat. No. 6,824,361 to Yu et al., it is known to decreasethe depth of the inlet channel at the end of the inlet channel such thatthe inlet channel may decrease in depth at a first constant rate over afirst distance and then taper at a second constant rate over a seconddistance such that the first rate is greater than the second rate.

What is needed is a fuel pump which minimizes or eliminates one or moreof the shortcomings as set forth above.

SUMMARY OF THE INVENTION

Briefly described, a fluid pump includes an inlet which introduces fluidinto the fluid pump; an outlet which discharges fluid from the fluidpump; a motor within the fluid pump; and a pumping member rotated by themotor about an axis such that rotation of the pumping member by themotor pumps fluid from the inlet to the outlet, the pumping member beingpositioned axially between an inlet plate which is stationary and anoutlet plate which is stationary. The inlet plate includes an inletplate flow channel in an inlet plate face of the inlet plate that facestoward the pumping member such that the inlet plate flow channelreceives fluid from the inlet, the inlet plate flow channel beingdefined by an inner wall and an outer wall. The inlet plate flow channelhas a first region and a second region, the first region extending overan angle of at least 150° and the second region extending from the firstregion over an angle of 61.8° to 71.8°. The inner wall has a firstradius which is constant over the first region and the second region,the first radius being centered about the axis. The outer wall has asecond radius which is constant over the first region and which iscentered about the axis. The outer wall also has a third radius which isconstant over the second region and which is not centered about theaxis. The arrangement of the second region minimizes the fluid hammereffect at the end of the inlet channel and also minimizes vibration ofthe inlet plate during operation, and consequently, noise generated bythe vibration of the inlet plate is also minimized.

BRIEF DESCRIPTION OF DRAWINGS

This invention will be further described with reference to theaccompanying drawings in which:

FIG. 1 is an exploded isometric view of a fuel pump in accordance withthe present invention;

FIG. 2 is an axial cross-sectional view of the fuel pump in accordancewith the present invention;

FIG. 3 is an exploded isometric view of a portion of the fuel pump inaccordance with the present invention;

FIG. 4 is an isometric view of a motor frame of the fuel pump inaccordance with the present invention;

FIG. 5 is an isometric view of the motor frame of FIG. 4 now shown in adifferent orientation;

FIG. 6 is an axial view of an inlet plate of the fuel pump in accordancewith the present invention;

FIG. 7 is an unfolded cross-sectional view of the inlet plate takenthrough section line 7-7 of FIG. 6;

FIG. 8 is an axial cross-sectional view of the inlet plate taken throughsection line 8-8 of FIG. 6; and

FIG. 9 is an unfolded cross-sectional view similar to FIG. 7 showing analternative arrangement.

DETAILED DESCRIPTION OF INVENTION

Reference will be made to FIGS. 1 and 2 which are an exploded isometricview and an axial cross-sectional view respectively of a fluid pumpillustrated as fuel pump 10 for pumping liquid fuel, for examplegasoline or diesel fuel, from a fuel tank (not shown) to an internalcombustion engine (not shown). While the fluid pump is illustrated asfuel pump 10, it should be understood that the invention is not to belimited to a fuel pump, but could also be applied to fluid pumps forpumping fluids other than fuel. Fuel pump 10 generally includes a pumpsection 12 at one end, a motor section 14 adjacent to pump section 12,and an outlet section 16 adjacent to motor section 14 at the end of fuelpump 10 opposite pump section 12. A housing 18 of fuel pump 10 retainspump section 12, motor section 14 and outlet section 16 together. Fuelenters fuel pump 10 at pump section 12, a portion of which is rotated bymotor section 14 as will be described in more detail later, and ispumped past motor section 14 to outlet section 16 where the fuel exitsfuel pump 10.

Motor section 14 includes an electric motor 20 which is disposed withinhousing 18. Electric motor 20 includes a shaft 22 extending therefrominto pump section 12. Shaft 22 rotates about an axis 24 when an electriccurrent is applied to electric motor 20. Electric motor 20 will bedescribed in greater detail later.

With continued reference to FIGS. 1 and 2, pump section 12 includes aninlet plate 26, a pumping member which is illustrated as an impeller 28,and an outlet plate 30. Inlet plate 26 is disposed at the end of pumpsection 12 that is distal from motor section 14 while outlet plate 30 isdisposed at the end of pump section 12 that is proximal to motor section14. Both inlet plate 26 and outlet plate 30 are fixed relative tohousing 18 to prevent relative movement between inlet plate 26 andoutlet plate 30 with respect to housing 18. Outlet plate 30 defines aspacer ring 32 on the side of outlet plate 30 that faces toward inletplate 26. Impeller 28 is disposed axially between inlet plate 26 andoutlet plate 30 such that impeller 28 is radially surrounded by spacerring 32. Impeller 28 is fixed to shaft 22 such that impeller 28 rotateswith shaft 22 in a one-to-one relationship. Spacer ring 32 isdimensioned to be slightly thicker than the dimension of impeller 28 inthe direction of axis 24, i.e. the dimension of spacer ring 32 in thedirection of axis 24 is greater than the dimension of impeller 28 in thedirection of axis 24. In this way, inlet plate 26, outlet plate 30, andspacer ring 32 are fixed within housing 18, for example by crimping theend of housing 18 proximal to outlet plate 30. Axial forces created bythe crimping process will be carried by spacer ring 32, therebypreventing impeller 28 from being clamped tightly between inlet plate 26and outlet plate 30 which would prevent impeller 28 from rotatingfreely. Spacer ring 32 is also dimensioned to have an inside diameterthat is larger than the outside diameter of impeller 28 to allowimpeller 28 to rotate freely within spacer ring 32 and axially betweeninlet plate 26 and outlet plate 30. While spacer ring 32 is illustratedas being made as a single piece with outlet plate 30, it should beunderstood that spacer ring 32 may alternatively be made as a separatepiece that is captured axially between outlet plate 30 and inlet plate26.

Inlet plate 26 is generally cylindrical in shape, and includes an inlet34 that extends through inlet plate 26 in the same direction as axis 24.Inlet 34 is a passage which introduces fuel into fuel pump 10. Inletplate 26 also includes an inlet plate flow channel 36 formed in an inletplate face 26a of inlet plate 26 that faces toward impeller 28. Inletplate flow channel 36 is in fluid communication with inlet 34. Inletplate 26 and inlet plate flow channel 36 will be described in greaterdetail later.

Outlet plate 30 is generally cylindrical in shape and includes an outletplate outlet passage 40 that extends through outlet plate 30 in the samedirection as axis 24. Outlet plate outlet passage 40 is in fluidcommunication with outlet section 16 as will be describe in more detaillater. Outlet plate 30 also includes an outlet plate flow channel 42formed in the face of outlet plate 30 that faces toward impeller 28.Outlet plate flow channel 42 is in fluid communication with outlet plateoutlet passage 40. Outlet plate 30 also includes an outlet plateaperture, hereinafter referred to as lower bearing 44, extending throughoutlet plate 30. Shaft 22 extends through lower bearing 44 in a closefitting relationship such that shaft 22 is able to rotate freely withinlower bearing 44 such that radial movement of shaft 22 within lowerbearing 44 is substantially prevented. In this way, lower bearing 44radially supports a lower end 46 of shaft 22 that is proximal to pumpsection 12.

Impeller 28 includes a plurality of blades 48 arranged in a polar arrayradially surrounding and centered about axis 24 such that blades 48 arealigned with inlet plate flow channel 36 and outlet plate flow channel42. Blades 48 are each separated from each other by a blade chamber 49that passes through impeller 28 in the general direction of axis 24.Impeller 28 may be made, for example only, by a plastic injectionmolding process in which the preceding features of impeller 28 areintegrally molded as a single piece of plastic.

Outlet section 16 includes an end cap 50 having an outlet 52 fordischarging fuel from fuel pump 10. Outlet 52 may be connected to, forexample only, a conduit (not shown) for supplying fuel to an internalcombustion engine (not shown). Outlet 52 is in fluid communication withoutlet plate outlet passage 40 of outlet plate 30 for receiving fuelthat has been pumped by pump section 12.

With continued reference to FIGS. 1 and 2 and with additional referenceto FIGS. 3 and 4, electric motor 20 includes a rotor or armature 54 witha plurality of circumferentially spaced motor windings 56 and acommutator portion 58, a motor frame 60, a pair of permanent magnets 62,and a flux carrier 64. Each magnet 62 is in the shape of a segment of ahollow cylinder. Motor frame 60 includes a top section 66 that isproximal to outlet section 16, a plurality of circumferentially spacedlegs 68 extending axially from top section 66 toward pump section 12,and a base section 70 axially spaced apart from top section 66 by legs68. Top section 66, legs 68, and base section 70 are preferablyintegrally formed from a single piece of plastic, for example only, by aplastic injection molding process.

Top section 66 of motor frame 60 includes a first electrical terminal 72and a second electrical terminal 74 extending therefrom and protrudingthrough end cap 50. First electrical terminal 72 and second electricalterminal 74 are arranged to be connected to a power source (not shown)such that first electrical terminal 72 and second electrical terminal 74are opposite in polarity. First electrical terminal 72 and secondelectrical terminal 74 may be disposed within pre-formed openings in topsection 66 or first electrical terminal 72 and second electricalterminal 74 may be insert molded with top section 66 when motor frame 60is formed by a plastic injection molding process. First electricalterminal 72 is in electrical communication with a first carbon brush 76while second electrical terminal 74 is in electrical communication witha second carbon brush 78. First carbon brush 76 is disposed within afirst brush holder 80 that is defined by top section 66 and is urgedinto contact with commutator portion 58 of armature 54 by a first brushspring 82 that is grounded to end cap 50. Second carbon brush 78 isdisposed within a second brush holder 84 defined by top section 66 andis urged into contact with commutator portion 58 of armature 54 by asecond brush spring 86 that is grounded to end cap 50. First carbonbrush 76 and second carbon brush 78 deliver electrical power to motorwindings 56 via commutator portion 58, thereby rotating armature 54 andshaft 22 about axis 24.

Top section 66 of motor frame 60 defines an upper bearing 88 thereinwhich radially supports an upper end 90 of shaft 22 that is proximal tooutlet section 16. Shaft 22 is able to rotate freely within upperbearing 88 such that radial movement of shaft 22 within upper bearing 88is substantially prevented.

Legs 68 are preferably equally circumferentially spaced around topsection 66 and base section 70 and define motor frame openings 92between legs 68. Motor frame openings 92 extend axially from top section66 to base section 70. One magnet 62 is disposed within each motor frameopening 92. Magnets 62 may be inserted within respective motor frameopenings 92 after motor frame 60 has been formed. Alternatively, magnets62 may be insert molted with motor frame 60 when motor frame 60 isformed by a plastic injection molding process. In this way, magnets 62and legs 68 radially surround armature 54. While two legs 68 and twomagnets 62 have been illustrated, it should be understood that otherquantities of legs 68 and magnets 62 may be used.

Base section 70 may be annular in shape and connects legs 68 to eachother. Base section 70 includes a base section recess 94 extendingaxially thereinto from the end of base section 70 that faces away fromtop section 66. Base section recess 94 is coaxial with upper bearing 88and receives outlet plate 30 closely therein such that radial movementof outlet plate 30 within base section recess 94 is substantiallyprevented. Since base section recess 94 is coaxial with upper bearing88, a coaxial relationship is maintained between lower bearing 44 andupper bearing 88 by base section 70. Base section 70 also defines anannular shoulder 96 that faces toward top section 66. Annular shoulder96 may be substantially perpendicular to axis 24.

Flux carrier 64 is made of a ferromagnetic material and may take theform of a cylindrical tube. Flux carrier 64 closely radially surroundslegs 68 of motor frame 60 and magnets 62. Flux carrier 64 may be made,for example only, from a sheet of ferromagnetic material formed to shapeby a rolling process. The end of flux carrier 64 that is proximal tobase section 70 of motor frame 60 axially abuts annular should 96 ofbase section 70 while the end of flux carrier 64 that is proximal to topsection 66 of motor frame 60 axially abuts a portion of end cap 50 thatradially surrounds top section 66 of motor frame 60. In this way, fluxcarrier 64 is captured axially between end cap 50 and annular shoulder96 of base section 70.

Since motor frame 60 may be made as a single piece, for example only, bya plastic injection molding process, upper bearing 88 and base sectionrecess 94 can be made by a single piece of tooling, thereby allowing ahigh degree of control over the relative positions of upper bearing 88and base section recess 94. Consequently, lower bearing 44 can moreeasily be maintained in a coaxial relationship with upper bearing 88.Similarly, since first brush holder 80 and second brush holder 84 may bedefined by top section 66, for example only, by an injection moldingprocess, first brush holder 80, second brush holder 84, and upperbearing 88 may be formed by a single piece of tooling, thereby allowinga high degree of control over the relative positions of first brushholder 80, second brush holder 84, and upper bearing 88. Consequently,first brush holder 80 and second brush holder 84 can be easilymaintained parallel to axis 24 which may be important for first carbonbrush 76 and second carbon brush 78 to adequately interface withcommutator portion 58 of armature 54.

Reference will now be made to FIGS. 6-8 which are respectively an axialview of inlet plate 26 looking toward inlet plate face 26a, an unfoldedcross-sectional view taken through section line 7-7 of FIG. 6, and anaxial cross-sectional view taken through section line 8-8 of FIG. 6. Theinventors have discovered geometry of inlet plate flow channel 36 whichminimizes fluid hammer effects and fluid pressure fluctuation withininlet plate flow channel 36, thereby minimizing vibration of inlet plate26 which can be propagated through fuel pump 10 and also minimizingaudible noise that results from the vibration of inlet plate 26propagating through fuel pump 10. Inlet plate flow channel 36 will bedescribed in greater detail in the paragraphs that follow.

As shown in FIG. 6, inlet plate flow channel 36 is generally arcuate inshape and includes an inlet region 98 at one end of inlet plate flowchannel 36, an outlet region 100 at the other end of inlet plate flowchannel 36, and an intermediate region 102 between inlet region 98 andoutlet region 100. Inlet plate flow channel 36 is defined by an innerwall 104, an outer wall 106 which is located radially outward of innerwall 104, and a bottom wall 108 which joins inner wall 104 and outerwall 106.

Inlet region 98 extends over approximately 30° of inlet plate flowchannel 36. Inlet 34 extends axially through inlet plate 26 at inletregion 98; consequently, fluid is introduced into inlet plate flowchannel 36 at inlet region 98 through inlet 34. At least a portion ofbottom wall 108 within inlet region 98 is oblique to inlet plate face26a as can best be seen in FIG. 7. Consequently, bottom wall 108 withininlet region 98 eases the change in direction of fuel flow from axiallythrough inlet 34 to laterally through inlet plate flow channel 36.

Intermediate region 102 extends over the majority of inlet plate flowchannel 36 and extends over at least 150°, and preferably extends about215° as illustrated herein. Inner wall 104 within intermediate region102 is defined by a radius R₁₀₄ where inner wall 104 intersects inletplate face 26 a such that radius R₁₀₄ is constant over intermediateregion 102 and is centered about axis 24. As shown in FIG. 8, inner wall104 may be arcuate in cross-section shape across the width of inletplate flow channel 36 within intermediate region 102. Similarly, outerwall 106 within intermediate region 102 is defined by a radius R_(106a)where outer wall 106 intersects inlet plate face 26 a such that radiusR_(106a) is constant over intermediate region 102 and is centered aboutaxis 24 and such that radius R_(106a) is greater than radius R₁₀₄. Asshown in FIG. 8, outer wall 106 may be arcuate in cross-section shapeacross the width of inlet plate flow channel 36 within intermediateregion 102. Intermediate region 102 may be defined by an intermediateregion first section 102 a and an intermediate region second section 102b such that intermediate region first section 102 a is located betweeninlet region 98 and intermediate region second section 102 b.Intermediate region first section 102 a and intermediate region secondsection 102 b are substantially the same except for their respectivedepths, i.e. the distance that bottom wall 108 is located axially frominlet plate face 26 a. More specifically, the axial distance from bottomwall 108 within intermediate region first section 102 a to inlet plateface 26 a is greater than the axial distance from bottom wall 108 withinintermediate region second section 102 b to inlet plate face 26 a.Consequently, a step 110 is defined by bottom wall 108 at the transitionfrom intermediate region first section 102 a and intermediate regionsecond section 102 b.

Outlet region 100 extends over a range of 61.8° to 71.8° of inlet plateflow channel 36 and is preferably about 66.8°. Inner wall 104 withinoutlet region 100 is defined by radius R₁₀₄ where inner wall 104intersects inlet plate face 26 a such that radius R₁₀₄ is constant overoutlet region 100 and is centered about axis 24. Consequently, innerwall 104 is defined by radius R₁₀₄ within intermediate region 102 andoutlet region 100. As shown in FIG. 8, inner wall 104 may be arcuate incross-section shape across the width of inlet plate flow channel 36.Outer wall 106 within outlet region 100 is defined by a radius R_(106b)where outer wall 106 intersects inlet plate face 26 a such that radiusR_(106b) is constant over outlet region 100. However, radius R_(106b) iscentered about a center point 112 which is not coincident with axis 24,consequently, radius R_(106b) is not centered about axis 24. RadiusR_(106b) is preferably less than radius R_(106a) and center point 112 ispreferably offset laterally from axis 24 in a direction that is towardintermediate region 102 and toward outlet region 100, i.e. down and tothe right as oriented in FIG. 6. In this way, outer wall 106 convergesto inner wall 104 within outlet region 100. It should be noted that atermination radius 113 may join inner wall 104 and outer wall 106 at theend of outlet region 100 which is distal from intermediate region 102,i.e. the end of outlet region 100 which terminates inlet plate flowchannel 36, such that termination radius 113 is less than about 15% ofradius R_(106b) while still considering inner wall 104 to have aconstant radius over outlet region 100 and while still considering outerwall 106 to have a constant radius over outlet region 100 and whilestill considering outer wall 106 to converge to inner wall 104. As shownin FIG. 8, outer wall 106 may be arcuate in cross-section shape acrossthe width of inlet plate flow channel 36. The depth of inlet plate flowchannel 36, i.e. the distance that bottom wall 108 is located axiallyfrom inlet plate face 26 a, preferably decrease over the entire lengthof outlet region 100. As shown in FIG. 7, bottom wall 108 tapers at aconstant rate from the end of outlet region 100 that is proximal tointermediate region 102 to the end of outlet region 100 that is distalfrom intermediate region 102, thereby defining a bottom wall taperedsection 114. Alternatively, as shown in FIG. 9, bottom wall taperedsection 114 may include an initial tapered section 114 a that isproximal to intermediate region 102 a final tapered section 114 b thatis distal from intermediate region 102 such that initial tapered section114 a tapers toward inlet plate face 26 a at greater rate than finaltapered section 114 b. However, initial tapered section 114 a and finaltapered section 114 b together taper the entire length of outlet region100 just like bottom wall tapered section 114 shown in FIG. 7. It shouldbe noted that both initial tapered section 114a and final taperedsection 114 b taper at constant rates.

In operation, inlet 34 is exposed to a volume of fuel (not shown) whichis to be pumped to, for example only, an internal combustion engine (notshown). An electric current is supplied to motor windings 56 in order torotate shaft 22 and impeller 28. As impeller 28 rotates, fuel is drawnthrough inlet 34 into inlet plate flow channel 36. Fuel within inletplate flow channel 36 flows through inlet region 98, intermediate region102, and outlet region 100. Blade chambers 49 allow fuel from inletplate flow channel 36 to flow to outlet plate flow channel 42, primarilyfrom outlet region 100. Impeller 28 subsequently discharges the fuelthrough outlet plate outlet passage 40 and consequently through outlet52. The inventors have discovered that defining inner wall 104 withradius R₁₀₄ over intermediate region 102 and outlet region 100 togetherwith defining outer wall 106 with radius R_(106a) over intermediateregion 102 and radius R_(106b) over outlet region 100 allows the fuel tobe efficiently directed out of inlet plate flow channel 36, therebyminimizing the interaction between the fuel and the end of inlet plateflow channel 36 which would tend to cause vibration of inlet plate 26that can propagate through fuel pump 10 and would also tend to cause afluid hammer effect. Consequently, vibration of inlet plate 26 isminimized, thereby also minimizing noise generated by the vibration ofinlet plate 26.

While this invention has been described in terms of preferredembodiments thereof, it is not intended to be so limited, but ratheronly to the extent set forth in the claims that follow.

We claim:
 1. A fluid pump comprising: an inlet which introduces fluidinto said fluid pump; an outlet which discharges fluid from said fluidpump; a motor within said fluid pump; and a pumping member rotated bysaid motor about an axis such that rotation of said pumping member bysaid motor pumps fluid from said inlet to said outlet, said pumpingmember being positioned axially between an inlet plate which isstationary and an outlet plate which is stationary; said inlet plateincludes an inlet plate flow channel in an inlet plate face of saidinlet plate that faces toward said pumping member such that said inletplate flow channel receives fluid from said inlet, said inlet plate flowchannel being defined by an inner wall and an outer wall wherein: saidinlet plate flow channel has a first region and a second region, saidfirst region extending over an angle of at least 150° and said secondregion extending from said first region over an angle of 61.8° to 71.8°;said inner wall has a first radius which is constant over said firstregion and said second region, said first radius being centered aboutsaid axis; and said outer wall has a second radius which is constantover said first region and which is centered about said axis, said outerwall also has a third radius which is constant over said second regionand which is not centered about said axis.
 2. A fluid pump as in claim 1wherein said second region of said inlet plate flow channel has a firstend that is proximal to said first region and a second end which isdistal from said first region and terminates said inlet plate flowchannel.
 3. A fluid pump as in claim 2 wherein said outer wall convergesto said inner wall at said second end.
 4. A fluid pump as in claim 1wherein said third radius is less than said second radius.
 5. A fluidpump as in claim 1 wherein: said inlet plate flow channel is furtherdefined by a bottom wall which connects said inner wall to said outerwall; and said bottom wall tapers over the entirety of said secondregion, thereby varying the depth of said inlet plate flow channelwithin said second region.
 6. A fluid pump as in claim 5 wherein saidbottom wall tapers at a constant rate over the entirety of said secondregion.
 7. A fluid pump as in claim 6 wherein said bottom wall tapers atsaid constant rate over the entirety of said second region to said inletplate face.
 8. A fluid pump as in claim 5 wherein: said bottom wall hasan initial tapered section within said second region such that saidinitial tapered section is proximal to said first region; said bottomwall has a final tapered section within said second region such thatsaid initial tapered section is between said final tapered section andsaid first region; said initial tapered section tapers at a firstconstant rate from said first region to said final tapered section; andsaid final tapered section tapers at a second constant rate from saidinitial tapered section.
 9. A fluid pump as in claim 8 wherein: saidfirst constant rate is greater than said second constant rate.
 10. Afluid pump as in claim 9 wherein said final tapered section tapers fromsaid initial tapered section to said inlet plate face.
 11. A fluid pumpas in claim 1 wherein said third radius is centered about a center pointwhich is laterally offset from said axis toward said first region.
 12. Afluid pump as in claim 11 wherein said center point is offset from saidaxis toward said second region in addition to toward said first region.13. A fluid pump as in claim 1 wherein: said inlet plate flow channelhas an inlet region at one end of said inlet plate flow channel suchthat said first region is between said inlet region and said secondregion and such that said inlet opens into said inlet region; and saidsecond region terminates said inlet plate flow channel.